1. Field of the Invention
The present invention relates to a baseball, and particularly to a solid baseball.
2. Description of the Background Art
As for a baseball, it is desired to improve safety by decreasing the impact force when the baseball hits against a human body. For example, in Little League, the hardness and the restitution coefficient of a ball for hardball are defined to improve safety when younger children play baseball. According to the rules of Little League, the hardness of the baseball is defined such that a load when the baseball is compressed by 6.35 mm is less than 45 lbf (200.17 N). In addition, the restitution coefficient of the baseball when the baseball hits against an iron plate at a speed of 26.82 m/s is defined to be 0.45 to 0.55.
The low compression Baseball defined in the rules of Little League has been described above. As for the medium compression Baseball, however, the hardness of the baseball is defined such that the load when the baseball is compressed by 6.35 mm is 75 to 150 lbf (333.62 to 667.23 N). In addition, the restitution coefficient of the baseball when the baseball hits against the iron plate at a speed of 26.82 m/s is defined to be 0.50 to 0.55.
An usual ball for hardball is configured by spherically winding a wool yarn on a rubber core, further winding a cotton yarn thereon to make a surface smooth, and putting a cow leather thereon and sewing up the leather with a sewing thread. It should be noted that a ball for hardball having a structure different from that of this usual ball for hardball is proposed. Japanese Patent Laying-Open No. 2002-210043, for example, proposes a ball for hardball configured by wrapping a rubber core in an intermediate core made of urethane foam.
In addition to the ball for hardball, a ball for rubber-ball baseball is used as the baseball. The ball for rubber-ball baseball does not have a core and is formed to be hollow. Because of this hollowness, the impact force of the ball for rubber-ball baseball is small, and thus, safety is ensured.
The ball for rubber-ball baseball is formed to be hollow to decrease the impact force, and thus, a high level of safety is ensured. However, since the ball for rubber-ball baseball is formed to be hollow to decrease the impact force, the hit distance is shorter than that of the ball for hardball. Therefore, when the ball for rubber-ball baseball is hit with a bat, the hit distance equal to that of the ball for hardball cannot be obtained.
In addition, the ball for hardball disclosed in the above publication is formed such that a feeling when the ball is hit is almost the same as that of the usual ball for hardball, although the rubber core is wrapped in the intermediate core made of urethane foam. Thus, the ball for hardball disclosed in the above publication has the impact force equal to that of the usual ball for hardball. Therefore, in the ball for hardball disclosed in the above publication, it is not assumed to further improve safety as compared with the usual ball for hardball.